Our laboratory has been investigating the immunobiology of the Neisserial porin PorB for the last two decades and, through our work regarding its use as a vaccine candidate, we found that PorB had unique immune stimulatory abilities above and beyond its own potential use as a vaccine. This was due to its property as a pathogen associated molecular patter (PAMP) inducing significant antigen presenting cell activation via recognition by TOLL-like Receptor 2 (TLR2) along with heterodimerization with TLR1 (but not TLR6). More recent work from our laboratory has greatly enhanced our understanding of the breadth and mechanism of the immune stimulating activity of PorB and allowed comparison to other potential immune adjuvants, including both TLR and non-TLR ligands. PorB adjuvant activity is absolutely dependent on MyD88 expression and almost totally dependent on TLR2 expression as shown by immunizations of MyD88 or TLR2 knockout (KO) mice with PorB/Ovalbumin (OVA - as a test antigen). We have further demonstrated that PorB can enhance antigen uptake in dendritic cells (DC) and macrophages, along with improved APC trafficking to draining lymph nodes (Platt et al., submitted Journal of Immunology). In addition, immunizations of MyD88 conditional KO mice (MyD88 floxed mice) have shown that macrophage, B cell or DC MyD88 signaling is essential for PorB adjuvant activity. Moreover, we have demonstrated that PorB is a potent inducer of germinal center (GC) formation in spleens and lymph nodes of immunized mice, and this induction is MyD88 dependent. Surprisingly, we found that PorB/OVA immunization of macrophage specific MyD88 conditional KO mice failed to induce a robust germinal center response or anti-OVA antibody as normally seen in WT mice. This defect in antibody responses appears to be greater when compared to either B cell or DC MyD88 conditional KO mice, demonstrating that macrophages may be the most important APC involved with PorB adjuvanticity. Based on the information obtained from our preliminary data, we have developed the following aims to further delineate the mechanisms of adjuvant activity PorB and other TLR ligand based immune adjuvants. Aim 1 will examine the overall effect of PorB and other vaccine adjuvants on GC formation and function using OVA as a test antigen and Influenza Nucleoprotein as a pathogen related antigen; Aim 2 will investigate the ability of PorB and other adjuvants to directly influence SHM and antibody affinity; and Aim 3 will delineate the role and potential function of macrophages in the adjuvant activity of PorB, especially in relation to GC formation. Importantly, the impact of findings from the studies in thi proposal go beyond just describing the use of PorB as an adjuvant, but will elucidate here-to-fore under studied mechanisms for the induction of immune responses by immune adjuvants, in general, and will have a great bearing on our overall understanding regarding germinal center formation and effective vaccine responses.